Detection of specific changes in the blood of cancer patients is considered to be of great practical importance. Besides the theoretical interest raised by this question it represents also a hope for finding a paraclinical test of practical usefulness in the detection of the cancer disease as early as possible.
In the last decades a number of findings provided by various fields of medicine have been proposed as being indicative of the presence of the neoplastic condition. These data are related to qualitative and quantitative enzymatic changes which appear in the blood of cancer patients, such as variations in the titers of histaminase, lactic dehydrogenase or seric aldolase, or tumor specific or organ specific findings such as acid phosphatase, alkaline phosphatase or thyroid carcinoma products. All these various data have in common the postulate of a basic difference between the metabolism of the normal and the malignant cell, which difference is enzymatically detectable.
Other biological research has led to the finding, in the blood of cancer patients, of pathological proteins such as alpha 1 and alpha 2, and other paraproteins have also been identified. Recently, advances in immunology and refinements in immunodiagnostic techniques have led to the discovery of a large range of cancer markers, the best known of them being the oncofetal antigens (carcino embryonic antigen--CEA, alpha feto protein, AFP, pancreatic oncofetal antigen, beta oncofetal antigen,) or the series of placental antigens of the ectopic hormones recently discovered, and also the oncogenic viruses.
However, the practical value of these markers for diagnostic purposes is limited by the great number of false positive and false negative results which accompany the blood investigation performed on cancer patients and control groups. In spite of their multiplicity, none of the markers has been able to provide a satisfactory answer to the need for a cancer diagnostic test and a certain amount of reliable information may be obtained only by the use of a battery of biochemical tests.
In spite of the great diversity of the pathological factors found in the blood of cancer patients, their identification is made by means of biochemical or immunochemical methods only, and in no case is the functional value of the pathological products assessed. Actually, in spite of the very well-known clinical effects of the cancerous intoxication on the whole body (the paraneoplastic syndrome), no laboratory test has yet been found in which the humoral changes of cancer are checked by the functional effects induced on other living tissues.